The maximum of 23.9C on Sunday was all above average at +3.3C thanks to the sunshine that began to shine strongly around midday as the cloud began to thin. The warmth built up as the afternoon progressed, the peak was logged at 17.56. More cloud overnight meant a mild night that saw the thermometer not drop below 10.5C, logged at 05.01, which was 0.3C above my 40-year average and made it the warmest night since the 14th.
Monday revealed a misty, foggy start to the new day with the visibility slowly dropping to a minimum of 300mm around 07.30, after which time the sun got to work and by 08.00 patches of blue sky came into view through variable cloud.
The anticyclone will be with us for the next two days but on Wednesday the projection is for another depression to take over control of our weather.
There has been much mention in the press recently of a possible heatwave this week, perhaps the following might be of interest. The forecast for Wiltshire this week, if it is accurate, dose not indicate a heatwave.
Why do heatwaves happen?
Heatwaves are most common in summer when high pressure develops across an area. High pressure systems are slow moving and can persist over an area for a prolonged period of time, such as days or weeks. They can occur in the UK due to the location of the jet stream, which is usually to the north of the UK in the summer. This can allow high pressure to develop over the UK resulting in persistent dry and settled weather.
In England & Wales on Sunday, the Met Office issued a 4-day Heat Health Alert from 08.00 Monday 24th, a system which places each Local Authority region into one of four levels.
In March 2022 the Met Office announced that the official heatwave thresholds were being updated ahead of the summer, resulting in eight counties having their threshold increased by 1C. The heatwave threshold for Wiltshire was raised from 26C to 27C and must be equalled or exceeded for three consecutive days to be classed as a heatwave.
The original thresholds were derived from the distribution of July maximum temperatures in a 1981-2010 reference climate period and the change in threshold results from the Met Office update to a 1991-2020 reference climate.